Please enable JavaScript.
Coggle requires JavaScript to display documents.
Ch8: Roots, Taproot & Fibrous root systems: separate!, DneCdHkWwAMyx6c…
Ch8: Roots
Other Types of Roots/Root Modifications
Storage Roots
long term carbohydrate storage from summer photosynthesis
carbs stored are used to produce new shoots in the spring
Prop Roots
the stems of monocots can become wider, more vascular bundles
transport additional nutrients and water to the stem through the soil
they contract and place tension on the stem, acting as stabilizers
Aerial Roots of Orchids
many orchids are epiphytic, living attached to tree branches
adapted to drought conditions
velamen: orchid root epidermis, composed of several layers of dead, large cells
acts as a waterproof barrier
Mycorrhizae
at least 80% of seed plant roots form symbiotic relationships with soil fungi
ectomycorhizal relationship: most all woody plants
fungal hyphae penetrate the outermost root cortex cells but never invade the cells themselves
endomycorhizal relationship: herbaceous plants, fungi hyphae cannot pass the casparian strip
they branch repeatedly once inside
Roots of Strangler Figs
birds eat the strangler fig roots and the drop the seeds in trees
gains nutrients from rainwater until it meets the soil, then penetrates the soil and branches profusely
roots fuse together whenever they meet, branches around the host tree
the roots encircle the tree, "strangling" it
typically the host tree dies as a result
Haustorial Roots of Parisitic Flowering Plants
haustoria: roots of parasitic plants
not all haustoria are related to each other
haustoria must adhere firmly to its host through secretions or growing a small branch or root
after penetration, parasite cells make contact with the hosts xylem
a continuous vessel from host to parasite is formed
Root Nodules/Nitrogen Fixation
lack of soil nitrogen is one of the main growth limiting factors
nitrogen fixation: chemical conversion of atmospheric nitrogen into usable compounds
Internal Structure of Roots
Root Cap
the root grows through edges in the root cap
cells are small and meristematic, then develop dense starch grains
the cells detect gravity due to where the starch grains settle
Root Apical Meristem
quiescent center: mitotically inactive central region
these cells are more resistant to various types of harmful agents
cell divisions taking place
Zone of Elongation
just behind the apical meristem
cells expand greatly
mostly cells are enlarging in this region
outermost cells: protoderm/epidermis
innermost cells: provascular tissue that develops into xylem and phloem
farther from the root tip older cells develop into metaxylem and metaphloem
Zone of Maturation/Root Hair Zone
root hairs grow outward, increasing absorption of water/minerals
no distinct boundary between zone of elongation and zone of maturation
transport of minerals from epidermis to vascular tissue
endodermis: waterproof
casparian trips: bands of altered walls, control the types of minerals that enter the xylem water streams
most glands have casparian strips, preventing the glands secretions from seeping into the surrounding tissue
Mature Portions of the Root
passage cells: cells containing only casparian strips, found in the fairly mature parts of the root
continuous endodermis maturation leads to a watertight sheath around the vascular tissues to keep water in
root pressure: absorption of minerals in the root hair zone lead to a water pressure that builds up
External Structure of Roots
Organization of Root Systems
lateral roots(branch roots): smaller than the singular taproot (branches off)
lateral roots can produce more lateral roots
taproot
develops from the
radicle
(present in the seed, embryotic root)
usually becomes the largest root
carrots, beets, radishes, carb storage during winter
Fibrous root system:
most monocots & some dicots, a mass of many similarly sized roots
arises when the radicle dies during or right after germination
known as
adventitious roots
(increase absorption/transport capacities in the root system)
many eudicots: secondary growth perennials
most monocots cannot undergo secondary growth
Structure of Individual Roots
root tip is where growth in length occurs
growth by apical meristems
only the extreme tip pushes through the soil
root apical meristem: protected by the root cap, thick layer of cells
dictyosomes of root cap cells secrete mucigel
mucigel: lubricates passage through the soil
localized growth
just behind the root cap and root apical meristem is the zone of elongation
zone of elongation
: where cells undergo division and expansion
behind the zone of elongation is the root hair zone (many epidermal cells extend out as trichomes
root hairs do not occur in the zone of elongation
root hairs
greatly increase the roots surface area
behind the root hair zone is where new lateral roots emerge
Origin/Development of Lateral Roots
initiated by cell divisions in the pericycle
lateral roots destroy cells of the cortex and endodermis, breaking the endodermis
lateral roots have root caps
initiated from deep within the root
not developed at the surface like buds
Taproot & Fibrous root systems: separate!
